Pool Volume Calculator
Every chemical dose, equipment size and water bill starts with one number: how many gallons your pool holds. This calculator finds that number from your pool’s shape and dimensions, in gallons, liters and cubic feet, then turns it into the two answers pool owners ask for next: how long the fill takes at your hose rate, and exactly how much chlorine to add for your target ppm across four real product strengths. Once you know the gallons, the pool turnover rate calculator puts them to work on pump run times, and the pool flow rate calculator sizes the flow to match.
Dose = volume × ppm ÷ product strength. Always add chemicals per the product label and retest before swimming.
Doses are estimates for planning. Product labels govern: strengths drift as products age, and liquid chlorine loses strength in storage, especially in heat.
Quick Answer
A 32 × 16 ft rectangle sloping from 3 ft to 8 ft holds 21,065 US gallons (79,740 liters), with an average depth of 5.5 ft. At an 8 GPM hose the fill takes about 43.9 hours, and raising free chlorine by 2 ppm with 65% cal-hypo takes 8.7 oz of product. Enter your own shape and dimensions in the calculator for your pool's number.
Key takeaways
- Pool volume = surface area × average depth, then × 7.48052 to get US gallons. Average depth for a sloped floor is (shallow + deep) ÷ 2.
- Measure the water depth from the waterline down, not the wall height. Wall measurements can overstate the volume by up to a third.
- Kidney results are estimates: the 0.585 factor is a widely used industry approximation, and other conventions give different answers.
- Chlorine dose = ppm × liters ÷ product strength. A 20% volume error is a 20% dosing error.
How to use the calculator
Pick your pool shape and units, enter the dimensions and the two depths, and click Calculate. The fill-time and chlorine-dose helpers update live as you type in their boxes.
- Choose the shape: rectangle covers squares; round takes a diameter; oval takes the long and short axes; kidney takes the longest length and widest width. The kidney result uses the 0.585 area factor on the bounding rectangle, which the card labels as what it is, an estimate.
- Enter real water depths: shallow and deep ends measured from the waterline to the floor. If your pool has a flat bottom, enter the same depth twice.
- Read the audit trail: the results box shows the step-by-step arithmetic (surface area, average depth, cubic feet, gallons) so you can check the math by hand.
- Use the helpers: type your hose rate in GPM for the fill time, and your target ppm rise plus product for the chlorine dose. Doses for granular products show ounces and pounds; liquid chlorine shows ounces by weight and fluid ounces.
Results stay hidden until you click Calculate. Copy my results and Share results sit side by side under the results.
Pool volume formulas by shape
Every shape reduces to the same idea: surface area times average depth gives cubic feet, and one cubic foot holds 7.48052 US gallons. The shape only changes how the surface area is found.
Round: π × radius² × avg depth × 7.48052 = gallons
Oval: π × (length ÷ 2) × (width ÷ 2) × avg depth × 7.48052 = gallons
Kidney: length × width × avg depth × 0.585 × 7.48052 = gallons (estimate)
Average depth = (shallow end + deep end) ÷ 2
The 7.48052 factor is fixed arithmetic: a US gallon is defined as 231 cubic inches and a cubic foot holds 1,728 of them, so 1,728 ÷ 231 = 7.4805194…. Quick estimates often round to 7.5, which is fine for a water bill but not for chemical dosing, where the extra precision matters. The same rectangle formula with 7.5 appears in the Certified Pool Operator training materials, which also use the (shallow + deep) ÷ 2 average for constant-slope floors.
The two helpers use equally simple math. Fill time (hours) = gallons ÷ (GPM × 60). Chlorine dose: ppm × liters = milligrams of pure chlorine needed, divided by the product's strength gives milligrams of product, divided by 28,349.5 gives ounces. That is the same relationship pool operator guidance states as "multiply the concentration required by the pool volume in litres," adjusted for how much of the product is actually chlorine.
Worked example, then the other shapes
The pre-filled values reproduce the rectangle example exactly:
Every row below is a real run of this calculator, so you can switch the shape and type any of them in to get the same figures back:
| Shape and dimensions | Gallons | Liters |
|---|---|---|
| Rectangle 32 × 16 ft, 3-8 ft deep | 21,065 | 79,740 |
| Round 18 ft diameter, 4 ft deep | 7,614 | 28,823 |
| Oval 30 × 15 ft, 5 ft deep | 13,219 | 50,040 |
| Kidney 32 × 16 ft, 5 ft deep (0.585 factor) | 11,203 | 42,407 |
| Rectangle 9.75 × 4.88 m, 0.91-2.44 m deep | 21,054 | 79,697 |
And the helpers on the worked pool: an 8 GPM hose fills 21,065 gallons in 21,065 ÷ 480 = 43.9 hours (43h 53m). Raising free chlorine by 2 ppm needs 2 × 79,740 = 159,480 mg of pure chlorine; with 65% cal-hypo that is 245,354 mg of product = 8.7 oz (0.54 lb). Switch the product to 10% liquid chlorine and the same 2 ppm takes 56.3 oz by weight (46.5 fl oz).
Sanity-check your result against those bands. A backyard rectangle that lands at 200,000 gallons means a mistyped dimension, not a big pool.
The kidney problem: why 0.585 is an estimate, not a measurement
A kidney pool has no exact area formula, so the industry approximates. This tool multiplies the bounding rectangle (longest length × widest width) by 0.585. Other conventions exist: one widely used method multiplies (widest + narrowest widths) × length × 0.45 instead. On curvy pools those conventions can disagree by 20% or more, which is exactly why the tool prints the factor it used right in the audit line.
If your freeform pool has lobes, coves or a separate shallow shelf, the honest approach is the split-into-sections method: divide the pool into rectangles and circles, compute each volume with its own depth, and add them. Pool industry guidance recommends exactly that for complex bottoms, and it beats any single factor. For dosing, a 20% kidney uncertainty is still far better than the up-to-33% error from measuring wall height instead of water depth.
Why volume accuracy matters
Every chlorine dose is ppm × gallons, so a 20% volume error is a 20% dosing error. Undershooting leaves algae alive; overshooting wastes chemical and can bleach liners. Equipment sizing runs on the same number: pumps, filters and heaters are all rated against the volume they must move or warm. And if you are on metered water, the fill volume is the water bill.
Three habits keep the number honest. First, measure water depth from the waterline down, never the wall height; pools are rarely filled to the brim, and the difference overstates volume by up to a third. Second, use the real average depth on sloped floors rather than guessing the middle. Third, retest after dosing: even a careful volume is still an estimate, and the test kit is the final word. If evaporation keeps stealing water between top-ups, the evaporation rate water calculator quantifies that loss, and dosing dilutions for top-up chemistry are covered by the chemical dilution calculator.
What competing calculators miss
Most pool volume tools stop at gallons. They give you the number and leave you to figure out what to do with it, and a few make choices worth knowing about:
- Dosing tables that are not doses: one well-known volume calculator pairs its result with a per-10,000-gallon chemical table (shock, pH up, stabilizer, salt). Useful as a shopping list, but it cannot answer "how much 65% cal-hypo raises my pool by 2 ppm." This tool answers that directly, per product strength.
- Kidney conventions that disagree silently: some calculators use the 0.45 × (width A + width B) convention while this one uses 0.585 on the bounding rectangle, and neither page tells you the other exists. This page names the convention in the result line and explains the alternative above.
- Fill time treated as a separate product: a couple of pool blogs pair volume with a fill-time-and-cost calculator, but stop before chlorine. Getting volume, fill time and per-product dosing in one place, with the audit trail showing the arithmetic, is what this page does that they do not.
- No audit trail: single-number tools give you 21,065 gallons with no way to check it. The step line here (area, average depth, cubic feet, gallons) lets you verify every figure by hand.
- The gap this page fills: four shapes with honest kidney disclosure, feet-or-meters input, live fill-time and per-product chlorine dosing, and a step-by-step audit line, all in one card.
Pool volume FAQs
Multiply surface area by average depth in feet, then by 7.48052. A 32 × 16 ft rectangle with a 3-to-8 ft slope: 512 sq ft × 5.5 ft × 7.48052 = 21,065 gallons. Enter your shape and dimensions in the calculator for the exact figure.
Use the circle area: π × radius² × average depth × 7.48052. An 18 ft diameter pool at 4 ft average depth is π × 81 × 4 × 7.48052 = 7,614 gallons. Measure the diameter straight across at the widest point and halve it for the radius.
There is no exact formula, so the industry approximates. This calculator multiplies the bounding rectangle (longest length × widest width) by the 0.585 area factor, then by average depth and 7.48052. Treat the result as an estimate: other conventions give different answers, and complex freeforms are better split into sections.
For a constant slope, add the shallow-end and deep-end water depths and divide by 2. A pool sloping from 3 ft to 8 ft averages 5.5 ft. For abrupt drops or multi-level floors, split the pool into sections, compute each volume separately, and add them.
The water depth, always. Measure from the waterline down to the floor at each end. Pools are rarely filled to the brim, so wall height overstates the volume, sometimes by a third, and every dose computed from it is off by the same share.
Divide the gallons by your hose rate in GPM times 60. A 21,065-gallon pool at 8 GPM takes 21,065 ÷ 480 = 43.9 hours, about 43 hours and 53 minutes. Type your hose rate into the fill helper for your pool's time.
It depends on the product's strength: dose = ppm × liters ÷ strength. As a check, this calculator gives about 2.1 oz of 65% cal-hypo per 10,000 gallons for 1 ppm, matching the Illinois Department of Public Health's 2 oz rule of thumb. Always confirm with the product label and retest.
Because weight and volume differ for liquids. The dose math gives ounces by weight of product; liquid chlorine is denser than water, so the tool converts to fluid ounces (about 0.8265 fl oz per oz) for measuring with a cup. Either figure describes the same dose.
Add This Calculator to Your Website
Embed this calculator on your own site with the code below. Pick a size to preview it live, then copy the code.
Powered by Calculator Zilo
References
- VivoAquatics Certified Pool Operator training materials. CPO Calculations: pool volume formulas, average depth and turnover math. Accessed October 23, 2026.
- National Institute of Standards and Technology. Special Publication 811: Guide for the Use of the International System of Units (SI), Appendix B conversion factors. Accessed October 23, 2026.
- Pool Water Treatment Advisory Group (PWTAG). Superchlorination of swimming pool water (Technical Note): dose equals concentration required multiplied by pool volume in litres. Accessed October 23, 2026.
- Illinois Department of Public Health. Procedure for Hyperchlorination in Public Swimming Facilities: 2 oz of calcium hypochlorite per 10,000 gallons for a 1 ppm rise. Accessed October 23, 2026.
- Fluidra. Ideal chlorine levels for swimming pools: levels in ppm and table: ppm as mg per liter, and conversion by product available-chlorine percentage. Accessed October 23, 2026.